1. Field of the Invention
The present invention relates to sealing a rotor ring in a turbine stage of a turbomachine such as an airplane turbojet or turboprop.
2. Description of the Related Art
Typically, a turbomachine turbine comprises at least one stage having a nozzle made up of an annular row of stator vanes, followed by a rotor wheel mounted inside a sectorized ring. The downstream end of the nozzle has an annular rim that extends radially outwards and that carries fastener means for fastening to a casing of the turbine. The sectorized ring situated downstream therefrom has an upstream cylindrical ring that is held radially against a rail of the turbine casing by an annular locking member of C-shaped or U-shaped section that is engaged axially on the casing rail and on the cylindrical rim of the ring.
The cylindrical rim of the ring and the casing rail are generally thermally protected by an annular sheet that is mounted between the outer rim of the nozzle and the upstream end of the ring so as to limit the passage of gas from the turbine flow section radially outwards into the annular space housing the rim of the ring and the rail of the casing.
Nevertheless, sealing is not perfect and leaks of hot gas coming from the turbine flow section can cause the temperature of the casing fastener hooks to rise, thereby causing cracks or fissures to form that might destroy the hooks.
Furthermore, the nozzle vanes generally include flow channels for passing cooling air that is taken upstream from the compressor of the turbomachine.
It is known to take a fraction of the air flowing in the channels of these vanes and to reinject this air into the annular space for housing the upstream rim of the ring and the rail of the casing so as to lower their temperature. Injecting air into this space also serves to maintain pressure in this space that is higher than the pressure of the combustion gas passing through the turbine, thereby limiting the amount of said gas that penetrates into the annular space.
Nevertheless, when the sealing between the outer rim of the nozzle and the upstream end of the ring is not sufficient, the cooling air injected into the annular space housing the rim of the ring and the rail of the casing tends to pass radially inwards into the turbine flow section, and thus no longer contributes to cooling the casing and the ring.